1. Field of the Invention
The present invention relates to a speed change gear for an automatic transmission. The speed change gear has an arrangement of a speed reduction planetary gear set for reducing a rotation from a power source (engine and the like) and a latter speed change mechanism for inputting the thus reduced rotation. The speed reduction planetary gear set includes a ring gear having an outer periphery which is provided with a direct clutch for transmitting the rotation from the power source (engine and the like) to the latter speed change mechanism.
Moreover, the present invention relates to a technology for making a gear train smaller.
2. Description of the Related Art
For reduced fuel consumption and improved drivability, recently, an automatic transmission is likely to have the greater and greater number of gear shifts.
Japanese Patent Unexamined Publication No. P2000-55152 (=JP2000055152) discloses a conventional technology for reducing a gear noise by improving on-vehicle mountability. More specifically, the above improvement is made by preventing the automatic transmission (achieving six forward gears and one reverse gear) from becoming increased in axial length.
As is seen in FIG. 8, a speed change gear for an automatic transmission according to Japanese Patent Unexamined Publication No. P2000-55152 (=JP2000055152) has a speed reduction planetary gear set G1 and a counter gear 101 which are disposed in the vicinity of a front end (substantially in the center of the vehicle) of the transmission. The above speed reduction planetary gear set G1 is of a double pinion type which transmits a rotation from an input shaft 1 of the transmission to a direct clutch C3 via a planetary carrier PC1, with the direct clutch C3 disposed on an outer periphery of the speed reduction planetary gear set G1 and with the counter gear 101 disposed rearward (leftward in FIG. 8) relative to the speed reduction planetary gear set G1. With the above constitution, namely, disposing the speed reduction planetary gear set G1 and the counter gear 101 close to the front end (substantially the center of the vehicle) of the transmission can reduce the gear noise. In addition, overlapping members of the speed reduction planetary gear set G1 in the above constitution can reduce the transmission in overall length.
For increasing freedom (flexibility) of gear ratio of a final gear on the front end of the transmission, a differential ring gear (not shown) needs to secure a great outer diameter, relative to a distance between a main shaft and a differential shaft of a gear train.
The above overlapping constitution of members of the speed reduction planetary gear set G1 according to Japanese Patent Unexamined Publication No. P2000-55152 (=JP2000055152) includes the direct clutch C3 that has a clutch hub 102 disposed radially outward relative to a first ring gear R1 of the speed reduction planetary gear set G1, as is seen in FIG. 8. With the clutch hub 102 of the direct clutch C3, securing the great outer diameter of the differential ring gear (not shown) relative to the distance between the main shaft and the differential shaft of the gear train is of difficulty for the following reason:                In a radial direction of the gear train, an area is to be secured equivalent to thickness of the clutch hub 102 added by a gap between the clutch hub 102 and the first ring gear R1.        